Rangers FC has asked supporters yet again to refrain from refrains of a sectarian nature.
Manager Ally McCoist suggests a list of approved appropriate ditties.
It might be easier to compile a short leet of subjects to be avoided: religion, ethnicity and Irish history. The prohibitions would apply equally to adherents of Celtic.
The challenge is to find topics upon which the two sides can safely disagree. Obviously not politics – British, Scottish or Irish.
How about philosophy? With its many separate schools of thought, philosophy is a subject about which Old Firm fans can fall out without breaking any laws. (At least not until the Scottish Parliament passes a bill on philosophically aggravated assault.)
Over at Ibrox stadium, they will no doubt follow transcendental idealism as espoused by Immanuel Kant. Supporters who fill a 50,000-seat stadium for a third division match against East Stirling will surely appreciate there are fundamental features of reality that escape our direct knowledge because of the natural limits of the human faculties.
Down Parkhead way, existentialism may be hailed. Having watched the Celtic defence in action many fans will understand the Nietzschean characterisation of the existential attitude as a sense of disorientation and confusion in the face of an apparently meaningless or absurd world. Some fans will think Nietzsche is a Celtic transfer target in the Bundesliga.
There is a flaw in my logic since philosophy is too cerebral a subject for the level of vituperation required in football songs and chants. Geography is usually a good reason for rivalry. Supporters are supposed to cherish the local club and have a high level of animosity towards the team even slightly further away. This concept may not work in Bridgeton and other enclaves of Glasgow's east end.
A down-to-earth topic such as food should be fertile territory for supporter song and banter. Who ate all the pies? You've never seen a salad. Sadly, in Glasgow, debate would quickly turn to potatoes and the famine and we're back at sectarian square one.
Mobile phones might be the answer. Let's have a huge and bitter divide about the relative merits of the Android versus the iPhone.
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